Modern broadband communication networks rely on satellites to complement the terrestrial telecommunication infrastructure. Satellites accommodate global reach and enable world-wide direct broadcasting by facilitating wide access to the backbone network from remote sites or areas where the installation of ground segment infrastructure is not economically viable. At the same time the new broadband applications increase the bandwidth demands in every part of the network - and satellites are no exception. Modern telecom satellites incorporate On-Board Processors (OBP) having analogue-to-digital (ADC) and digital-to-analogue converters (DAC) at their inputs/outputs and making use of digital processing to handle hundreds of signals; as the amount of information exchanged increases, so do the physical size, mass and power consumption of the interconnects required to transfer massive amounts of data through bulk electric wires.

Multicore fiber enables a parallel optic data link with a single optical fiber, thus providing an attractive way to increase the total throughput and the integration density of the interconnections. We study and present photonics integration technologies and optical coupling approaches for multicore transmitter and receiver subassemblies. Such optical engines are implemented and characterized using multimode 6-core fibers and multicore-optimized active devices: 850-nm VCSEL and PD arrays with circular layout and multi-channel driver and receiver ICs. They are developed for bit-rates of 25 Gbps/channel and beyond, i.e. <150 Gbps per fiber, and also optimized for ruggedized transceivers with extended operation temperature range, for harsh environment applications, including space.

Even though the lane speed of VCSEL based AOC and transceivers has reached 25 Gbps and beyond [1-7], parallel optics are getting even more important in order to meet the increasing demand for aggregate bandwidths in upcoming applications, among others, 100 Gigabit Ethernet, Infiniband EDR, or EOM (embedded optical modules). As 100 Gbps can be achieved by, e.g., 4 times 25 Gbps using standard QSFP form factor, different approaches are using large scale 2D VCSEL arrays operating at lower lane speeds. Early work on 2D VCSEL based transceivers has already been presented beginning of this century [8] and recent work also addressed the potential of this technology [9,10]. In 2013, Compass EOS has introduced a 1.34 Tbps core router solution [11,12,13] that incorporates 2D VCSEL arrays of 14x12 emitters designed and manufactured by Philips U-L-M Photonics. The VCSEL array is mounted face down onto a CMOS ASIC, directly on top of the analog area. The emission wavelength of 1000 nm allows for substrate side emission and thus for flip-chip mounting as well as the possibility of integrating 2D microlens arrays onto the stack of CMOS and VCSEL array. After briefly introducing the router with regard to the incorporated VCSEL technology we discuss the design and performance of the VCSEL array. Finally, the assembly solution for this most compact and dense transceiver solution is presented.

In comparison to widely used InGaAs Quantum Wells (QW) in high speed VCSELs operating at 25 Gbps and beyond, we present an investigation on the use of GaAs QWs, which have proven their ability to serve reliably in 10 Gbps and 14 Gbps VCSEL products and allow for an evolutionary extension of data rates based on mature technology. As data centers continuously increase in size, the demand for longer reach optical links within these data centers is addressed by the proposal of using small spectral width single-mode VCSELs that offer the potential of significantly reduced chromatic dispersion along optical fibers of several 100 m length. Performance and modeling parameters of single-mode VCSELs are being compared to those of typical multi-mode VCSELs built from identical epitaxy and process technology.

Philips recently released a new VCSEL and photodiode product family for the fast growing FDR InfiniBandTM
generation. In this work we review the influence of production process variations on VCSEL characteristics, the FDR
VCSEL transmission behavior as well as wear-out reliability characteristics. Data collected during an initial 15 wafers
pilot production batch verify that FDR VCSEL manufacturing reached mature volume production level. The VCSEL for
the next EDR (26Gbps) InfiniBandTM generation is currently being developed at Philips. The paper presents
characteristics of the first EDR VCSEL iteration.

Data centers and supercomputers are driving the demand for short reach aggregate bandwidth. E.g. active CXP active
optical cables (AOC) with an aggregate bandwidth of 120 Gbps [1] are being installed since about one year in some of
the biggest server farms in the world. As these applications require parallel optics, obviously this is a natural playground
for VCSEL technology. The 10G VCSEL platform of Philips ULM Photonics is enabling operation of such AOC at less
than 3 W total power by low bias currents for the individual VCSEL as low as 3.4 mA at room temperature and 5.5 mA
at 85°C ambient. In combination with ideally matched driver electronics, the launch power of the VCSELs can be
stabilized within 0.15dB variation across this operating temperature range [2] and thus allow for open loop power
control. With more than 108 hours of operation in the field and no field return reported, the FIT rate for the 1x12
VCSEL array can be calculated to be less than 10 FIT.

Many VCSEL based applications require optical feedback of the emitted light. E.g. light output monitor functions in
transceivers are used to compensate for thermally induced power variation, power degradation, or even breakdown of
pixels if logic for redundancy is available. In this case integrated photodiodes offer less complex assembly compared to
widely used hybrid solutions, e.g. known in LC-TOSA assemblies. Especially for chip-on-board (COB) assembly and
array configurations, integrated monitor diodes offer a simple and compact power monitoring possibility. For 850 nm
VCSELs the integrated photodiodes can be placed between substrate and bottom-DBR, on top of the top-DBR, or
inbetween the layer sequence of one DBR. Integrated intra-cavity photodiodes offer superior characteristics in terms of
reduced sensitivity for spontaneously emitted light [1] and thus are very well suited for power monitoring or even endof-
life (EOL) detection. We present an advanced device design for an intra-cavity photodiode and according
performance data in comparison with competing approaches.

Over the past 3 years laser based tracking systems for optical PC mice have outnumbered the traditional VCSEL market
datacom by far. Whereas VCSEL for datacom in the 850 nm regime emit in multipe transverse modes, all laser based
tracking systems demand for single-mode operation which require advanced manufacturing technology. Next generation
tracking systems even require single-polarization characteristics in order to avoid unwanted movement of the pointer
due to polarization flips. High volume manufacturing and optimized production methods are crucial for achieving the
addressed technical and commercial targets of this consumer market. The resulting ideal laser source which emits
single-mode and single-polarization at low cost is also a promising platform for further applications like tuneable diode
laser absorption spectroscopy (TDLAS) or miniature atomic clocks when adapted to the according wavelengths.

Driving basic VCSEL technology in the '90, datacom has been the first volume market for various VCSEL products.
The downturn in 2001 can be regarded as a point in time, when engineers both from VCSEL manufacturers and nondatacom
users started to identify VCSEL technology as a very promising laser source platform for many other
applications. Dedicated spectroscopy laser sources based on VCSEL technology, e.g. for oxygen sensing [1], have
proven their competitiveness in industrial applications. The most prosepective consumer market of human-machineinterfaces
like laser mice has shown the huge potential of the VCSEL technology in low costs, high volume
applications, even given extreme technical performance specifications [2]. Just as a consequence, VCSELs are now
penetrating into the next potential volume markets, where unique properties of this technology is requested: High power
pulsed laser applications, where low cost is a key factor for market entry. In this paper we discuss a suitable
semiconductor technology platform, assembly solutions, selected applications and their market potential as well as
performance and reliability data. From small footprint of 0.3 mm2 and 0.11 mm2 peak output powers of 0.7 W and more than 6 W at 850 nm wavelength are shown at 30 &mgr;s and 30 ns pulse widths, respectively.

Up to now applications for singlemode VCSELs were in low volume and high prized applications like tunable diode laser absorption spectroscopy (TDLAS, [1,2]) or optical interferometers. Typical volumes for these applications are in the range of thousands of pcs per year, with pricing levels of several 100 USD/pcs. New applications for singlemode VCSELs in consumer markets require manufacturing in very high volumes and at very low cost. Examples are laser-based optical mouse sensors, optical encoders, and rubidium atomic clocks for GPS systems [3,4]. U-L-M photonics presents manufacturing aspects, device performance and reliability data for these devices. The first part of the paper is dealing with high volume manufacturing of 850 nm singlemode VCSEL chips with very high efficiency and low operation current. Special processing technologies have been developed to achieve yields on 3 inch wafers of more than 90%. Wafer qualification procedures are discussed as well. The second part of the paper covers high volume packaging in TO and SMT type packages where very high packaging yields must be achieved. In the last part of the paper reliability issues are discussed, focused on the very high susceptibility of these devices to electrostatic discharge.

The growing demand on low cost high spectral purity laser sources at specific wavelengths for applications like tuneable diode laser absorption spectroscopy (TDLAS) and optical pumping of atomic clocks can be met by sophisticated single-mode VCSELs in the 760 to 980 nm wavelength range. Equipped with micro thermo electrical cooler (TEC) and thermistor inside a small standard TO46 package, the resulting wavelength tuning range is larger than +/- 2.5 nm. U-L-M photonics presents manufacturing aspects, device performance and reliability data on tuneable single-mode VCSELs at 760, 780, 794, 852, and 948 nm lately introduced to the market. According applications are O2 sensing, Rb pumping, Cs pumping, and moisture sensing, respectively. The first part of the paper dealing with manufacturing aspects focuses on control of resonance wavelength during epitaxial growth and process control during selective oxidation for current confinement. Acceptable resonance wavelength tolerance is as small as +/- 1nm and typical aperture size of oxide confined single-mode VCSELs is 3 &mu;m with only few hundred nm tolerance. Both of these major production steps significantly contribute to yield on wafer values. Key performance data for the presented single-mode VCSELs are: >0.5 mW of optical output power, >30 dB side mode suppression ratio, and extrapolated 10E7 h MTTF at room temperature based on several millions of real test hours. Finally, appropriate fiber coupling solutions will be presented and discussed.

Following the success in fiber based DataCom, VCSELs start to conquer additional market shares in a variety of other
applications like free space optics (FSO), lighting, printing, and sensing. U-L-M photonics presents a new family of
commercial high power VCSELs emitting powers of up to 50 mW cw at RT based on top-emitting technology. The
devices are available at 850 nm emission wavelength. All devices can be operated passively cooled and provide
modulation bandwidths of up to 1 GHz. Wallplug efficiencies are in excess of 25 %. Even higher output power of 250
mW cw from a 80 μm active diameter bottom-emitting VCSEL operating at 980 nm has already been obtained although
just beeing passively cooled. Further power up scaling is achieved by arrangement of multiple VCSELs in 2D arrays.
For the first time we demonstrate cw output power of 10 Watt cw at RT from compact monolithic VCSEL module of 14
mm2 chip area. Transfer of the technology to other wavelengths, e.g. 808 nm and 945 nm, is presented, too, and shows
perspectives towards homogeneous optical pumping of solid state lasers. Almost identical device performance levels
can be presented for the entire wavelength span. All discussed results are based on highest quality epitaxy optimized for
maximum intrinsic efficiency and differential slope efficiency. Oxide confinement is used for current constriction that
provides most efficient electrical pumping of the active area. In combination with advanced mounting techniques all
mentioned aspects sum up to allow for cost effective VCSEL products in the medium and high power laser regime. The
circular output beam in addition to simple heat sinking offers attractive solutions for advanced system integration.

There is a wide variety of reasons why future high-performance datacom links are believed to rely on two-dimensional VCSEL arrays suitable for direct flip-chip hybridization. Some typical are as follows: highest interconnect density, high-frequency operation, self alignment for precise mounting, productivity at high number of channels per chip. In this paper the latest approaches to flip-chip VCSELs are presented. In particular we will asses the properties of transparent substrate VCSEL arrays which are soldered light-emitting side up as well as VCSEL arrays which are soldered light-emitting side down, e.g., onto a CMOS driver chip. The VCSEL arrays are designed for bottom- or top-emission at 850 nm emission wavelength and modulation speeds up to 10 Gbps per channel.

U-L-M photonics GmbH has been set up to develop next-generation vertical-cavity surface-emitting laser (VCSEL) products and to exploit the full potential of these industry-leading devices in terms of performance and application areas. Reliability is important for all application areas for VCSELs. This paper presents the excellent reliability characteristics of U-L-M’s VCSEL technology. Accumulation of all advantageous properties VCSELs are famous for, like low power consumption, circular low divergent beam profile, high modulation bandwidth, and scalability of monolithic arrangements, results in two-dimensional (2D) VCSEL arrays that appear as key components to reach highest aggregate bandwidths of tomorrow’s parallel optical transceivers. We report on 2D VCSEL arrays, substrate emitting although operating at 850 nm and prepared for flip-chip bonding, that are well suited for the customer’s needs in terms of speed, power consumption, and compact integration. Up to now, in most single channel transceivers, the VCSEL is packaged in a TO can and connected to the driver via a printed circuit board. We investigate the performance of a high speed VCSEL in a TO 46 package and demonstrate 10 Gbps transmission. The potential of VCSEL technology in other areas of application than datacom or telecom is just going to be exploited. We present a 760 nm single-mode VCSELs for gas monitoring applications.

We report on recent progress in the design of short-wavelength vertical-cavity surface-emitting lasers (VCSELs) for 10 Gbit/s datacom applications. Topics of interest include differential mode delay characterizations of high-performance multimode fibers and their interplay with transverse single- and multimode VCSELs, flip-chip integrated two-dimensional arrays at 850 nm wavelength, as well
as experiments toward the realization of optical backplanes. In
the latter case, reliable 10 Gbit/s data transmission has been
achieved over low-loss integrated polymer waveguides with up to 1
meter length. Moreover we present VCSELs with output powers in the 10 mW range that are employed in multi-beam transmitters for free-space optical data transmission with Gbit/s speed over distances of up to about 2 km.

Accumulation of all advantageous properties VCSELs are famous for, like low power consumption, circular low divergent beam profile, high modulation bandwidth, and scalability of monolithic arrangements, results in two-dimensional (2D) VCSEL arrays that appear as key components to reach highest aggregate bandwidths of tomorrow's parallel optical transceivers. We report on 2D VCSEL arrays, substrate emitting although operating at 850 nm and prepared for flip-chip bonding, that are well suited for the customer's needs in terms of speed, power consumption, reliability and compact integration. Based on advanced technology, our arrays target the requirements of transceivers in the OC-192 VSR and 10 Gigabit Ethernet arena. In this paper we present the basic technology, static and dynamic device characteristics as well as reliability data for a 4x12 850 nm bottom-emitting VCSEL array. A13

Architectural studies have identified field-programmable gate arrays (FPGA) as a class of general-purpose very large scale integration components that could benefit from the introduction at the logic level of state-of-the-art massively parallel optical inter-chip interconnections. In this paper, we present a small-scale optoelectronic multi-FPGA demonstrator in which three optoelectronic enhanced FPGAs are interconnected by 2D Plastic Optical Fiber (POF) ribbon arrays. The full-custom FPGA chips consisting of an 8 X 8 array of very simple programmable logic cells are equipped with two optical sources and two receivers per FPGA cell yielding a maximum of 256 optical links per chip. The optical links are designed for signaling rates of 80 to 100 Mbit/s (160 to 200 Mbaud using Manchester coded data) compatible with the maximum clock frequency of the, in 0.6 micrometers CMOS implemented, FPGA chips. The results of parallel link experiments between such modules with both VCSELs and LEDs as sources will be shown. A large scale parallel bit error rate experiment at 90 Mbit/s/channel between two half-populated VCSEL-based FPGA modules with 112 of their 128 channels operational at bit error rates below 10-13 on all active channels (approximately equals 10 Gbit/s/chip) proves the feasibility of this approach. We first briefly discuss the general architecture and the realization of the optoelectronic FPGA demonstrator system. We then present measurement results on the available modules, followed by some conclusions on this work.

We report on the fabrication of two-dimensional vertical- cavity surface-emitting laser (VCSEL) arrays designed for flip-chip integration with silicon complementary metal-oxide semiconductor (CMOS) circuits. Devices emitting at 980 nm wavelength show single-mode output powers of 3 mW, modulation current efficiencies up to 10 GHz/(root)mA, and are suitable for digital data transmission at 12.5 Gb/s. The chips are incorporated into optical area interconnect system demonstrators employing plastic optical fiber bundles as waveguiding medium. Substrate removal is applied as a possible route toward the production of modules compatible to the standard 850 nm wavelength regime. Fully pretested and mechanically robust arrays for short-wavelength bottom emission are alternatively demonstrated by providing light outcoupling holes in the GaAs substrate.

In the implementation of optical data links, issues of power consumption, bandwidth and sensitivity have to be addressed in the design of optoelectronic components. This is especially important in high density parallel applications where large amounts of heat can cause thermal problems and performance degradation. We present two-dimensional vertical-cavity surface-emitting laser (VCSEL) arrays for high density optical interconnects.
Devices emit at 850 or 980\,nm wavelength and exhibit excellent operation data. The VCSEL chips are used - within the framework of the European research project OIIC - in multiple CMOS-to-CMOS link demonstrators.
In this paper we discuss a 0.6 µm-CMOS VCSEL transmitter with 32 data
channels whose power consumption is only 15.7 mW/ch at 1 Gb/s/ch data transmission.

It is our goal to demonstrate the viability of massively parallel optical interconnections between electronic VLSI chips. This is done through the development of the technology necessary for the realization of such interconnections, and the definition of a systems architecture in which these interconnections play a meaningful role. Field-programmable gate arrays (FPGA) have been identified as a class of general-purpose very large scale integration components that could benefit from the massive introduction of state-of-the-art optical inter-chip interconnections at the logic level. In this paper, we present the realization of a small-scale optoelectronic FPGA with 8 X 8 logic cells, containing two optical sources and two receivers per FPGA cell yielding a total of 256 links per chip. These FPGA chips designed to operate with information rates of 80 Mbit/s/link will be used in a three- chip demonstrator system as a test bed for the concepts above. We first identify the reason why we think optical interconnects can provide added value in FPGAs. The next sections briefly discuss the general architecture of our demonstrator system and the realization of the optoelectronic FPGA. We then present first measurement results followed by ongoing work and conclusions.

10We have investigated efficient light outcoupling from light- emitting diodes (LEDs) by introducing lateral tapers. The concept is based on light generation in the very central area of a circularly symmetric structure. After propagating between two highly reflecting mirrors light is outcoupled in tapered mesa region. By proper processing we achieve quantum and wallplug efficiencies of almost 30% for outcoupling via a planar surface or, respectively, 45% and 44% for encapsulated devices.

Oxide-confined vertical-cavity surface-emitting laser diodes (VCSELs) are optimized for multi-Gbit/s data rate optical transmission systems. Noise characteristics and small-signal modulation response of high-performance transverse single- and multi-mode devices under different operation conditions are investigated. We demonstrate for the first time 12.5 Gbit/s data rate fiber transmission with a bit-error rate of better than 10-11 for pseudo-random bit sequence signals over 100m multimode fiber and 1 km single-mode fiber. Maximum electrical and optical bandwidths obtained at 3 mA driving current are 12 GHz and 13 GHz, respectively. For pumping levels above 2.8 times threshold current, the relative intensity noise is below -150 dB/Hz up to 5 GHz for output powers of about 1mW. In detail, we investigate the low frequency intensity noise of high efficiency small area selectively oxidized VCSELs emitting in the fundamental transverse mode up to 7 times threshold current at room temperature and in multiple transverse modes up to 20 times threshold current. For low temperature operation quantum efficiency of the VCSEL is increased leading to photon- number fluctuations 1.4 dB below the shot noise limit. This is to our best knowledge the largest amount of squeezing ever reported for VCSELs.

We have designed and fabricated a 64 channel optical module using a self-alignment flip-chip packaging technique for 2D GaAs epitaxial-side emitting vertical-cavity surface- emitting laser (VCSEL) array mounting without substrate removal on Si subcarrier. Light emission is obtained through a wet-chemically etched window in the Si subcarrier. The 2D independently addressable selectively oxidized GaAs laser array is arranged in an 8 X 8 matrix with a device pitch of 250 micrometers and each laser is supplied with two individual top contacts. This metallization scheme allows flip-chip mounting junction-side down on Si subcarrier. The VCSEL array chip is placed above the window in the Si subcarrier and is assembled using a self-aligned bonding technique with PbSn solder bumps. Arrays with 4 micrometers active diameter investigated before and after packaging show quite homogeneous optical and electrical continuous wave output characteristics exhibiting threshold currents of less than 1.1 mA and single-mode output powers of 2 mW. Driving characteristics of the lasers in the array are fully compatible to advanced 3.3 V CMOS technology. The modules are used to demonstrate free-space directional transmission applying beam steering.

We present a non-resonant light emitting diode with a novel concept of light outcoupling. Light is generated in the center of a radially symmetric structure and propagates between two mirrors of a tapered region where outcoupling occurs. Principles of outcoupling are given using a simple ray tracing model. Different process routes are developed resulting in on-substrate as well as substratless devices. Not yet optimized devices show quantum efficiencies of 12% and 15%, respectively.

We have designed and fabricated 1 X 8 and 4 X 8 VCSEL arrays at 850 nm and 980 nm operation wavelength, respectively, which are designed for maximum single-mode output power and high frequency applications. GaAs VCSELs in the 1 X 8 array show record high single-mode CW powers up to 4.8 mW. Individual devices of the 4 X 8 InGaAs VCSEL array exhibit small signal modulation bandwidths exceeding 10 GHz.

We have designed and fabricated 4 X 8 vertical-cavity surface-emitting laser (VCSEL) arrays intended to be used as transmitters in short-distance parallel optical interconnects. In order to meet the requirements of 2D, high-speed optical links, each of the 32 laser diodes is supplied with two individual top contacts. The metallization scheme allows flip-chip mounting of the array modules junction-side down on silicon complementary metal oxide semiconductor (CMOS) chips. The optical and electrical characteristics across the arrays with device pitch of 250 micrometers are quite homogeneous. Arrays with 3 micrometers , 6 micrometers and 10 micrometers active diameter lasers have been investigated. The small devices show threshold currents of 600 (mu) A, single-mode output powers as high as 3 mW and maximum wavelength deviations of only 3 nm. The driving characteristics of all arrays are fully compatible to advanced 3.3 V CMOS technology. Using these arrays, we have measured small-signal modulation bandwidths exceeding 10 GHz and transmitted pseudo random data at 8 Gbit/s channel over 500 m graded index multimode fiber. This corresponds to a data transmission rate of 256 Gbit/s per array of 1 X 2 mm2 footprint area.

My Library

You currently do not have any folders to save your paper to! Create a new folder below.

Keywords/Phrases

Keywords

in

Remove

in

Remove

in

Remove

+ Add another field

Search In:

Proceedings

Volume

Journals +

Volume

Issue

Page

Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews